Reflective displays

Cholesteric LCs can act as hosts for dyes to produce coloured displays (see section 5.2.2.1 below) " their temperature dependent colour change has found applications in thermochromic inks, °" and as pigments and copy safe colours their selective reflecting capabilities have been applied in colours and filters for reflective displays and projection systems, " reflective polarisers and their electrical field induced switching in displays and smart reflectors, in colour patterning for full-colour recording. ... 

For example, active-matrix backplanes for reflective displays using electrophoretic media is a potential application for large-area electronics. Electrophoretic media are usually charged colored particles suspended in an insulating fluid [35-37]. When the fluid is held in an electric field between two conductive plates, the particles will move between the plates creating a dark or a reflective state. Because the contrast in an electrophoretic display is because of reflection, no backlight is required and the display has relatively low-power consumption compared with a transmissive liquid-crystal display. 

A PLZT reflective display is similar in appearance to the common liquid crystal display (LCD). The structure of the device is shown schematically in Fig. 8.16 a suitable PLZT composition is the slim-loop quadratic 9.5/65/35. 

For the second harmonic generation, we find that above a certain input intensity a dynamics reminiscent of a competitive, multi-wave mixing process occurs the pump field is mostly reflected, revealing a novel type of optical limiting behavior, while forward a nd b ackward g eneration i s g enerally b alanced. W e a Iso s tudy t he case of parametric down-conversion, where an intense second harmonic signal is injected in order to control a much weaker fundamental beam. Our results reveal the onset of a new process that has no counterpart in bulk materials both transmission and reflection display an unexpected, unusual, resonance-like effect as functions of input second harmonic power. 

Yang D K, Huange X Y, Zhu Y M. 1997. Bistabel cholesteric reflective displays materials and drive schemes. Annu Rev Mater Sci 27 117 146. 

Electrochromic materials is a remarkable and productive research area over the last three decades since it has potential applications in smart window products, e-papers, optical shutters, transmissive and reflective displays, self-darkening mirror devices, and optical memories. The electrochromic effect has been observed in metal oxides (e.g., WO3),... 

FIGURE 32.24 Basic layout of a PLZT reflective display. 

Drzaic P (2006) Reflective displays the guest for electronic paper. J Soc Inf Disp Seminar M-8... 

Yang DK, Doane JW (1992) Cholesteric liquid crys-tal/polymer gel dispersion reflective display application. SID Symp Dig Tech Pap 23 759-761... 

Gaily BJ (2004) Wide-Gamut color reflective displays using iMoDTM interference technology. SID Symp Dig Tech Pap 35 654—657... 

Yang DK (2005) Flexible bistable cholesteric reflective displays. J Display Technol 2 32-37... 

Beni and Hackwood [29] although a demonstrable prototype concept was only produced in 2003 by Hayes and Feenstra [30]. The principle is illustrated in Fig. 10a. A dyed oil drop under a transparent aqueous solution is confined within a cell that represents a single pixel in the reflective display the cell is placed atop a white substrate. A hydrophobic layer is coated at the bottom of the cell such that in the absence of an applied potential, the oil forms a thin equilibrium layer covering the entire cell area. Upon application of the electric field, however, the contact angle increases, and the oil film retracts to form a drop in the comer of the cell. The extent to which the drop retracts is thus dependent on the applied voltage. The 250 pm pixels are also believed to be sufficiently small such that an area average is only apparent to the observer the retracted spot... 

The electrodes used in the ECDs are dependent on the type of device absorptive/transmissive (window type) or absorptive/reflective. Typical electrodes are the transparent conductors such as ITO, fluorine-doped tin oxide (Sn02 F), and PEDOT/PSS for the absorptive/transmissive window-type ECDs and reflective metals such as gold in reflective display-type devices. Single-walled carbon nanotubes (SWNTs) have emerged as an alternative to transparent electrodes such as ITO, with comparable transparency in the visible region and far superior transparency in the wavelength range of 2-5 p,m [258]. 

It should be noticed that, when crossed polarizers are used, as in reflective displays, the intensities are complementary to those shown in Fig. 1. We will, however, use the definitions of the parallel-polarizer case. 

The other case is that of a reflective display where a hemispherical illumination of the display is assumed this is taken into account by using the definition Voff=Vc. We have not attempted to consider intermediate situations because the angular variation is very complicated and the definition of Voff and Vqj becomes rather arbitrary. 

Figure 9 shows the effect of the variation of Ac from zero to twenty while keeping at five. For transmissive displays, the dependence is weak. For reflective displays, it is stronger and a low value of Ae is to be preferred. 

Fig. 6. Computed dependence of perceived contrast ratio on cell thickness for a reflective display with three different guest-host dyes having the indicated dichroic ratios R. Dye concentration adjusted to maintain an on-state brightness of 50%. Concentration of chiral dopant adjusted to maintain 3 turns of the cholesteric helix in the cell.

Fig. 7. Reflected display brightness versus perceived contrast ratio for three guest-host dyes having the indicated dichroic ratios. Increasing the concentration of the dye generally decreases the display brightness and increases the contrast ratio. Values used for this computation ng=1.76, nQ=1.50, d/p 3.0 and d=10.0 ym.

Fig, 2, C-V curves measured in the real image region of a reflective display. 

For outdoor applications, the displayed images of a transmissive LCD could be washed out by sunlight A reflective LCD would be a better choice. However, such a reflective display is unreadable in dark ambient conditions. Transflective LCDs integrate the features... 

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